Coating system for improved leading edge erosion protection

ABSTRACT

A gas turbine engine includes airfoils. At least a portion of the airfoils are coated with a coating that provides for erosion and corrosion protection for the portion of the airfoils.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalPatent Application No. 61/779,722, filed 13 Mar. 2013, the disclosure ofwhich is now incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to coatings, and morespecifically to coating systems to reduce erosion and corrosion in gasturbine engines.

BACKGROUND

Gas turbine engines are used to power aircraft, watercraft, powergenerators, and the like. Gas turbine engines typically include acompressor, a combustor, and a turbine. The compressors and turbine ofthe turbine engine can include turbine disks or turbine shafts, as wellas a number of blades mounted to the turbine disks/shafts that extendradially outwardly therefrom into the gas flow path. Also included inthe turbine engine are rotating, as well as static, seal elements thatchannel the airflow used for cooling certain components such as turbineblades and vanes. The airflow channeled by these rotating, as well asstatic, seal elements carry corrodant deposits to the turbine blades. Asthe maximum operating temperature of the turbine engine increases, theturbine blades are subjected to higher temperatures. Debris entering theengine can present issues for the compressor and other components.

Alkaline sulfate, sulfites, chlorides, carbonates, oxides, and othercorrodant salt deposits can be sources of erosion and corrosion. Inaddition, ingested dirt, fly ash, volcanic ash, concrete dust, sand, seasalt, etc. are a major source of erosion. This can lead to failure orpremature removal and replacement of the compressor blades unless thedamage is reduced or repaired. Conventional plasma vapor deposition(PVD) processes such as cathodic arc and E-beam PVD are widely usedmethods for depositing erosion resistant coatings on the airfoils ofcompressor blades and vanes. However, PVD processes such as cathodic arcand E-beam PVD typically introduce high residual stress on the leadingedge of the compressor airfoils during the coating process. When highresidual stress from the coating process is coupled with out-of-planestress from the leading edge geometry and thermal expansion mismatchbetween coating and substrate, it can result in coating spallation inthe as-coated condition providing insufficient leading edge erosionprotection.

Coating methods and coating compositions for compressor blades and vanesthat provide high angle solid particle erosion protection on the leadingedge of compressor airfoils are desired. Coating methods and coatingcompositions that also provide lower angle solid particle erosionprotection on the concave and convex sides of the airfoils are desired.

SUMMARY

The present application discloses one or more of the features recited inthe appended claims and/or the following features which, alone or in anycombination, may comprise patentable subject matter.

A coating system in accordance with the present disclosure may includethe application of an erosion resistant coating to a portion of a gasturbine engine blade. In some embodiments, the coating may be applied toa preselected exterior surface of the airfoil blades. The coating may beapplied to the leading edge surface of the airfoil to increase theerosion resistance of the leading edge. The coating may also be appliedto the concave side surface, the convex side surface, or combinationsthereof.

In some embodiments, the coating may be formed from tungsten-tungstencarbide, tungsten carbide cobalt, cobalt-chrome-tungsten carbide, chromecarbide-nickel, chrome carbide-nickel-chrome, or a diamond like carbonmaterial. The process may also include a metallic bond coat layerpositioned between the coating and the surface of the airfoil. Thesurface of the airfoil may also be nitrided or carburized before theapplication of the coating.

In some embodiments, the coating may be applied to the airfoil usinghigh velocity oxygen fuel spray, high velocity air fuel spray, solutionplasma spray, cold spray, chemical vapor deposition, electo sparkdeposition, plasma enhanced chemical vapor deposition, or air plasmaspray method.

These and other features of the present disclosure will become moreapparent from the following description of the illustrative embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a turbine with portions broken away toshow the vanes within the turbine;

FIG. 2 is a perspective view of a vane segment showing a series ofairfoils;

FIG. 2A is a perspective view of a series of compressor blades with eachcompressor including an airfoil;

FIG. 3 is a sectional view taken along lines 3-3 of FIG. 2 showing anairfoil having the coating of the present disclosure formed on theleading edge of the airfoil;

FIG. 4 is a sectional view of an airfoil having the coating of thepresent disclosure formed on a surface of the leading edge of theairfoil;

FIG. 5 is a sectional view of an airfoil having the coating of thepresent disclosure formed on the leading edge and concave side of theairfoil;

FIG. 6 is a sectional view of an airfoil having the coating of thepresent disclosure formed on the leading edge and the concave and convexsides of the airfoil;

FIG. 7 is a sectional view of an airfoil having the coating of thepresent disclosure formed on the leading edge on an airfoil that hasbeen nitrided or carburized and treated with a metallic bond coat layer.

FIG. 8 is a photograph of an airfoil sample showing erosion of theleading edge of the airfoil due to sand ingestion;

FIG. 9 is a photograph of another airfoil sample showing erosion to theleading edge of the airfoil; and

FIG. 10 includes photographs of test samples showing erosion of theleading edge of airfoil samples.

DETAILED DESCRIPTION OF THE DRAWINGS

For the purposes of promoting an understanding of the principles of thedisclosure, reference will now be made to a number of illustrativeembodiments illustrated in the drawings and specific language will beused to describe the same.

The present disclosure is directed to a coating system that provides anenhanced airfoil 14 including leading edge erosion protection for aturbine 11, as shown in FIGS. 1-2A. More particularly, the presentdisclosure is directed to one or more coatings that provide enhancedhigh angle solid particle erosion protection on compressor airfoils 14,as shown, for example, in FIGS. 3-7. The coating is primarily applied tothe leading edge 12 of the airfoils 14, as shown in FIGS. 3, 4, and 7.The coating(s) may also provide low angle solid particle erosionprotection on the concave 16 and convex 18 sides of the airfoils 14, asshown in FIGS. 5 and 6.

The coating 31, for example, formed on the leading edge 12 of theairfoils 14 is selected from group consisting of tungsten-tungstencarbide, tungsten carbide cobalt, cobalt-chrome-tungsten carbide, chromecarbide-nickel, chrome carbide-nickel-chrome, and diamond like carbon.The coating 31 on the leading edge 12 is preferably applied by use of ahigh velocity oxygen fuel (HVOF) spray, a high velocity air fuel (HVAF)spray, a solution plasma spray, a cold spray, chemical vapor deposition(CVD), electro spark deposition, plasma enhanced chemical vapordeposition (PE-CVD), or air plasma spray method. By applying the coating31 primarily to the leading edge 12, weight increase of the airfoils 14is minimized. The coating 31 also provides increased corrosionresistance.

In one illustrative embodiment, airfoil 14 may have first coating 31applied to leading edge 12 while a second coating 32 is applied to bothconcave surface 16 and convex surface 18 as shown in FIG. 3. In anotherillustrative embodiment, airfoil 14 may have first coating 31 applied toleading edge 12 while second coating 132 is applied over first coatingand on both concave and convex surfaces 16 and 18 as shown in FIG. 4. Instill yet another illustrative example, airfoil 14 may have a coating231 applied to both leading edge 12 and concave surface 16 whileomitting any coating on convex surface 18 as shown in FIG. 5. In anotherillustrative embodiment, airfoil 14 may have a coating 331 applied toleading edge 12, concave surface 16, and convex surface 18 as shown inFIG. 6. In still yet another illustrative example, airfoil 14 may have afirst coating 431 applied to leading edge 12, concave surface 16, andconvex surface 18 and a second coating 432 applied over first coating431 at leading edge 12.

In still yet another example, airfoil 14 may have a first coatingapplied to leading edge 12, a second coating applied to concave surface16, and a third coating applied to convex surface 18. The first, second,and third coatings may be all the same, all different, or any suitablecombination thereof.

In addition, the first coating may be applied to leading edge 12,concave surface 16, and convex surface 18. One or more coatings may beapplied over the first coating on one or more of the leading edge 12,concave surface 16, and convex surface 18. In some examples, the firstcoating may be the same or different than the one or more coatings.

The coatings 31, 32, 132, 231, 331, 431, 432 discussed previously areselected from the group consisting of TiAlN, AlTiN, TiAlN/TiNmultilayer, TiAlN/Cr multilayer, tungsten-tungsten carbide, tungstencarbide cobalt, cobalt-chrome-tungsten carbide, chrome carbide-nickel,chrome carbide-nickel-chrome, and diamond like carbon. The coatings 31,32, 132, 231, 331, 431, 432 may be applied by applied by PVD, HVOF,HVAF, solution plasma spray, cold spray, CVD, electro spark deposition,or PE-CVD.

Conventional PVD processes such as cathodic arc and E-beam PVD arewidely used methods for depositing erosion resistant coatings. However,PVD processes such as cathodic arc and E-beam PVD typically introducehigh residual stress on the leading edge of the compressor airfoilsduring the coating process. When high residual stress from the coatingprocess is coupled with out-of-plane stress from the leading edgegeometry and thermal expansion mismatch between coating and substrate,it can result in coating spallation in the as-coated condition andinsufficient leading edge erosion protection during engine operation.Coatings applied by HVOF, HVAF, solution plasma spray, cold spray, CVD,electro spark deposition, and PE-CVD can introduce lower residualstresses on the leading edge 12 of the compressor airfoil 14 when theright coating materials are used, which leads to better high angle solidparticle erosion protection on the leading edge 12.

If coating spray methods such as HVOF, HVAF, solution plasma spray, andcold spray are used, a powder size less than 50 μm is used normally toobtain a smooth surface finish. The powder size is preferably smallerthan 20 μm to obtain the desired finish on the airfoil 14. For both theleading edge coatings 12 and the convex 18 and the concave 16 sidecoatings, Ni, Ti, Cr, or other metallic bond coat layers 24 can be usedbetween the coatings and the airfoil 14. The surface of the airfoil 14can be nitrided and carburized 431 before the application of the coating432 to improve corrosion and erosion resistance, as shown, for example,in FIG. 7.

In one example, the thickness of the coating 31, 231, 331, 432 on theleading edge 12 is from about 10 μm to about 100 μm. In another example,the thickness of the coating 31, 231, 331, 432 on the leading edge 12 isfrom about 35 μm to about 75 μm. The thickness of the coating 32, 132,231, 331 on the concave 16 and convex side 18, for example, is fromabout 5 μm to about 50 μm. In another example, the thickness of thecoating 32, 132, 231, 331 on the concave 16 and convex 18 sides is fromabout 15 μm to about 35 μm. The thickness of the metallic bond coatlayer 431, for example, is from about 2.5 μm to about 10 μm. Thenitrided or carburized depth on the airfoil 14, for example, is fromabout 10 μm to about 50 μm.

FIG. 8 is a photograph of an airfoil sample showing erosion of theleading edge of the airfoil due to sand ingestion. In this photograph,the leading edge 12 of the airfoil 14 was coated with TiN applied bycathodic arc physical vapor deposition (PVD). As can be seen the LeadingEdge Preferential Erosion (LEPER) is present and is detrimental to gasturbine performance. Another airfoil sample showing erosion to theleading edge of the airfoil is shown in FIG. 9. The leading edge 12 ofthe airfoil 14 was treated with TiAlN applied by cathodic arc physicalvapor deposition (PVD). As can be seen, Leading Edge PreferentialErosion (LEPER) is present in the edge of the airfoil.

A series of photographs of erosion test result samples are shown in FIG.10 from testing performed by the University of Cincinnati. In thesetests, the leading edges of the airfoil samples were subjected to aparticulate applied in a series of stages. In the first stage, 0.995 Kgof 95% Arizona Road Dust (ARD) A4 (silica based sand with 80 μm nominaldiameter) with 5% Mil E-5007C crushed quartz (75˜100 μm) was used. Thephotographs taken at stage one indicate the amount of erosion that hasoccurred to the leading edge of the test samples. The samples weresubjected to multiple stages of erosion testing including a ninth stagewhere 1.1 Kg of ARD A4 was used. The photographs taken at stage nineindicate the amount of erosion that occurred to the leading edge of thetest samples. As can be seen, the tungsten carbide tungsten (WC/W)sample applied with the chemical vapor deposition (CVD) method shows aclean edge with no erosion. The coating microstructure is tungstencarbide (WC) particles dispersed in tungsten (W).

While the disclosure has been illustrated and described in detail in theforegoing drawings and description, the same is to be considered asexemplary and not restrictive in character, it being understood thatonly illustrative embodiments thereof have been shown and described andthat all changes and modifications that come within the spirit of thedisclosure are desired to be protected.

What is claimed is:
 1. A method for coating a portion of a gas turbineengine blade, the method comprising the steps of providing a gas turbineblade, the blade further comprising an airfoil section having anexterior surface and applying a coating layer to a preselected exteriorsurface selected from the group consisting of the leading edge surface,the concave side surface, the convex side, and combinations thereof, thecoating layer selected from the group consisting of tungsten-tungstencarbide, tungsten carbide cobalt, cobalt-chrome-tungsten carbide, chromecarbide-nickel, chrome carbide-nickel-chrome, and diamond like carbon,wherein the coating layer at the leading edge surface has a thicknessfrom about 10 μm to about 100 μm.
 2. The method of claim 1, wherein thecoating layer at the leading edge surface has a thickness from about 35μm to about 75 μm.
 3. The method of claim 2, wherein the coating layerat the concave and convex surfaces is from about 5 μm to about 50 μm. 4.The method of claim 1, further including the step of applying a metallicbond coat layer to the exterior surface of the airfoil before thecoating layer.
 5. The method of claim 4, wherein the metallic bond coatlayer has a thickness from about 2.5 μm to about 10 μm.
 6. The method ofclaim 5, wherein the metallic bond coat layer is selected from the groupconsisting of Ni, Ti, and Cr.
 7. The method of claim 1, furtherincluding the step of nitriding the surface of the airfoil.
 8. Themethod of claim 7, wherein the nitrided depth is from about 10 μm toabout 50 μm.
 9. The method of claim 1, further including the step ofcarburizing the surface of the airfoil.
 10. The method of claim 9,wherein the carburized depth is from about 10 μm to about 50 μm.
 11. Themethod of claim 1, wherein the coating is applied using coating spraymethods from the group consisting of HVOF, HVAF, solution plasma spray,electo spark deposition, and cold spray.
 12. The method of claim 11,wherein the coating powder size is less than 50 μm.
 13. The method ofclaim 12, wherein the powder size is less than 20 μm.